Tailoring water networks for anisotropic proton transport and hydroxyl-induced hopping in electrocatalytic hydrogen...

The dynamics of interfacial water adjacent to metal surfaces critically govern electrocatalytic processes, yet atomic-level control over charge and mass transfer remains elusive. Herein, we demonstrate that external electric fields (E-fields) enhance the hydrogen evolution reaction (HER) by reorganizing the interfacial hydrogen-bond (HB) network and optimizing hydroxyl adsorption. Under E-fields, a more ordered HB architecture emerges, characterized by enhanced vertical connectivity that facilitates anisotropic Grotthuss proton hopping. Moreover, hydroxyl species serve as electronically favorable proton acceptors, initiating intermolecular proton exchange within the inner Helmholtz plane (IHP) and facilitating spatially extended water dissociation across the Pt surface. The applied E-fields trigger interfacial charge redistribution, which weakens hydroxyl adsorption and thereby accelerates the Volmer step. These structural and electronic changes are accompanied by distinct ionic relaxation behaviors in the IHP and outer Helmholtz plane (OHP), reflecting their differing local water structures and dynamic responses. Collectively, these synergistic effects result in improved HER kinetics, as evidenced by significantly reduced Tafel slopes and increased turnover frequency. This study introduces a new design paradigm for electrocatalytic interfaces that extends beyond conventional catalyst engineering.